US1968874A - Dry kiln - Google Patents

Description

J. F. COBB Aug. 7, 1934.

DRY KILN Filed June 18, 1931 3 Sheets-$heet l 1 M (m -A BY y WM- ATTORNEY J. F. COBB Aug. 7, 1934.

DRY KILN Filed June 18, 1931 3 Sheets-Sheet 2 mw.v .-m o 1 0 1 1% g m wh ATTORNEY J. F. COBB DRY KILN Aug. 7, 1934.

Filed June 18, 1931 5 Sheets-Sheet 3 ATTORNEYX Patented Aug. 7, 1934 DRY KILN James Forrest Cobb, Portland, Oreg. Application June 18, 1931, Serial No. 545,345

8 Claims.

My invention relates to improvements in kilns having a main drive for actuating one or more transverse shafts on which one or more fans are mounted for driving the circulating medium in the kiln transversely to the length of the kiln in continuing cross circulation through interstices provided in the stock loads.

An important object of my invention is to balance or substantially equalize the throw of the fans and thereby effect greater uniformity of circulation throughout the kiln. In other word, my invention is contrived to cause a novel counteraction oitransverse circulatory currents of air within the kiln, with the result of effecting a more uniform general circulation.

Another object of my invention is to provide novel driving means for accomplishing the results desired.

Another object of my invention is to effect counteracting currents by novel means in both forward and reverse directions of air circulation transversely within the kiln, and thereby to accomplish a greater uniformity of distribution of the circulation through the interstices of the stock loads.

Another object of my invention is to effect a better mixing of the gaseous contents of the kiln by effecting some longitudinal circulation between the medial portions and the ends of the kiln in either direction of circulation in addition to the :general transverse circulation above mentioned. Another object of my invention is to provide novel compensation means for permitting the 33 incidental expansion and contraction of a drive shaft for one or more fans.

What constitutes my invention will be hereinafter specified in detail and succinctly defined in the appended claims.

In the accompanying drawings, in which my invention is illustrated in present preferred form of embodiment,

Figure I is a plan view of a kiln in which fans are illustrated as located above the material to be dried.

Figure II is a longitudinal vertical section on the line II-II of Figure I. p

Figure III is a transverse vertical section on lines III-III of Figures Iand II, respectively.

Figure IV is a plan view of another form of kiln modified in respect to disposition of the fans below the material to be dried.

Figure V is a longitudinal vertical section on the line VV of Figure IV.

Figure V1 is a transverse vertical section on the lines VI-VI of Figures IV and V, respectively.

Figure VII is a side elevation of a gear and its support complete with compensating means for permitting expansion of a drive shaft upon which said gear'is mounted.

Figure VIII is a front elevation of the subject matter shown in Figure VII.

Figure IX is a side elevation of another form of embodiment of a gear drive for the Ian, illustrating modified compensating means for permitting variation of the length of the drive shaft.

Figure X is a front view of the subject matter of Figure IX.

Figure 2G is a side elevation of a modified means for providing compensation for expansion and contraction of a common drive shaft for a series of fans.

Figure XII is an end elevation of the subject matter of Figure XI, looking from right to left.

Figure XIII is an end elevation of a kiln showing an individual motor drive for one of the fans located above the stock loads under a gabled type or stream lined roof.

Figure XIV is a side elevation of a portion of the type of coupling shown in Figure XI.

Figure XV is a side elevation of a modification of means for providing compensation for expansion and contraction of a common drive shaft for series of fans.

Referring to the numerals on the drawings:

1 indicates a kiln floor, 2 and 3 its side walls, and. 4 its roof. 5 indicates a non-indispensible intermediate partition disposed horizontally between the fioor 1 and the roof 4, which is shown in Figure III as above, and in Figure VI as below the stock load. 6, wherever it appears, is a partially diagrammatic illustration of a stock load or loads of material to be dried. 9 and 10, Figure V, indicate doors which, being disposable at discretion at either one or both ends of the ltriln, are kept closed while the kiln is in operaion.

The stock loads 6 are stacked in any suitable manner preferred. For example, they may be loaded upon bunks 12 which are supported as by dry kiln trucks 13 that may travel on track rails 14 provided for their accommodation within the kiln. The rails 14 may rest upon track. supports 15 which may be cross ties resting on the ground or floor 1, or may be'c'ross beams supporting the tracks above the floor 1, as shown in Figure V.

The stock loads 6 are preferably stacked by at 20 and 21,

aid of stickers 16 placed between layers of the stock in such manner as to provide interstices 1'7 between adjacent layers so as to permit free air circulation within the kiln therebetween.

Heating means within the kiln are indicated They may be of any suitable form of embodiment or location whether commonly known in the art or not.

I employ circulation compelling equipment comprising, for example, fans 25 and 26,-25 being used to designate right hand fans and 26 being used to designate left hand fans. These fans are operatively mounted, for example, on transverse shafts 27 and 28 which may be carried by bearings 30 and 31 provided on hearingstands 33 and 34 (see Figure VI, for example). The bearings are provided with means of lubrication such, for example, as suitable oil cups 35 which may be, as preferred, either of the wick-feed type or of the duct-feed type. One of the bearings 30 or 31 should be adapted to take end-thrust. In some cases, such as shown, for instance, in Figures, I, II and III, I employ a combination of gears, 33, 39, 40, and 41, a case 44, bearings 46 and 4'7, and a support 48 for the longitudinal shaft 37 and transverse shafts 27.

The combination of bevel gears or bevel friction, for instance, or any suitable means, and their cases are designed, respectively, to operate right hand fans 25 and left. hand fans 26, respectively. Each gear case 44 accommodates preferably bevel gears 38, 39, and 41, which may be spiral bevel gears, or the equivalent thereof if preferred. The gears 88 and 40 are keyed or otherwise securedto the longitudinal shaft 37.

The gears 38, 39, v40 and 41, are assembled in pairs for imparting right hand or left hand direction of rotation to the shaft 2'7, as desired. A right hand set of gears may include a gear 38 fixed on the common drive shaft 37 and a gear 39 keyed or otherwise fixed to a driven shaft 27. The left hand assemblage of gears consists preferably of a spiral bevel gear 40 fixed to the drive shaft 37 and a driven gear 41 fixed to the transverse shaft 28 on which the left hand fan 26 is fixed.

The gears above mentioned may be substantially the same in all respects except that one assemblage of gears 38 and 39 is employed for driving right hand fans, and the other assemblage 40 and 41 is employed for driving left hand fans.

The fans 25 and 26 are preferably mounted upon transverse shafts in a partition 52 extending substantially the full length of the kiln. The partition 52 has openings 54 and 55 for the accommodation of the right and left hand fans, respectively, an they, are made sufficiently large to permit movem nt of the fans due to expansion and contraction of the shaft 37.

In my kiln, of whatever type it be and whether it comprises one or more compartments, the fans effect one circuit of circulation moving simultaneously transversely throughout the full length of. a compartment of the kiln in one direction or in the opposite direction. When the circulating medium is moving in one direction,

the right hand fans 25 turn clockwise and the left hand fans 26, although they blow in the same general direction, turn counterclockwise.

In the state of the art prior to my invention, all right hand fans, or all left hand fans, when mounted on transverse driving shaft, have been made to rotate in the same direction fo PIO- ducing one circuit of transverse circulation. The result of such arrangement in operation is an unequal transversely distributed circulation that is due to the throw or variable directional flow of air from all the fans in addition to the transverse air movement. The combined throw of all the fans tends to develop a greater volume and velocity of circulation locally within the kiln, which causes an uneven drying condition within thekiln that is objectionable.

In one form of embodiment of my invention I propose to use alternately disposed right and left hand fans, respectively, which are rotated, respectively, in opposite directions. The throw of one of the fans is, therefore, counteracted by the throw of the next adjacent fan to such an extent that a substantially transverse air circulation is effected within the kiln.

Right and left hand fans have been employed in kilns on one longitudinal shaft delivering counteracting currents \friom the respective fans towards each other in order to effect a distributed transverse circulation within the kiln. My invention is differentiated therefrom by the use of right and left hand fans, on separate transverse shafts, respectively, thereby eliminating the complication of the necessity for the use of zigzag walled ducts or other obstructions which tend to build up resistance and to,increase static pressure, thus decreasing circulative air flow. By using transverse driving shafts and right hand fans and left hand fans alternately disposed through the kiln and rotated in opposite direction, alternately, I am able to obtain maximum air circulating efiiciency, uniform distribution of transverse air circulation, a thorough mixing of the circulatory medium, including the fresh air which has been taken on the suction side of the fan, and a uniform distribution of humidity. from the source which supplies it, also a uniform distribution of the circulating medium in operative contact with the heating coils of the kiln, so as to uniformly heat, mix, and humidify the circulatory medium before it passes into drying contact with the stock.

In another embodiment of my invention, I propose to use a series of right hand fans at one end of the kiln and'a series of left hand fans at the other end of the kiln. The right hand fans are disposed in series to effect by counteraction of two or more series, one general circuit of transverse circulation within the kiln.

When the right or left hand fans are em-v ployed in series, the fan throw effects a resultant longitudinal trend of circulation toward the ends of the kiln or toward the medial portion from the ends in two circuits of circulation in addition to the general transverse circulation.

There are forms of embodiment of my inventaion in which I prefer to use one driving shaft 37 to rotate all the fans by means of gears preferably of the bevel type or other like means which may be right hand or left hand, and corresponding transverse shafts on which corresponding right and left hand fans are mounted, which will thus be rotated to the right or to the left, depending upon the arrangement of the said gears. The,.right hand gear 38 or the one rotating to the right or in clockwise direction of movement, will drive a right hand fan 25, and the left hand gear, 40, rotating to the left will drive a left hand fan 26. These right hand and left hand gears may be alternately disposed, or the right hand gears may be of expansion and contraction of the drive shaft 37, are provided, such, for example only, as sliding gears on the gear supports, or gear supports which may be pivoted to permit expansion or contraction of the shaft.

In some cases (see Figures IV, V, and VI) where a continuous shaft 37 drives a series of fans by means of gears having transverse shafts 27 and 28 at right angles to the longitudinal axis of the kiln, the shafts 2'7 and 28 may be supported by one or more bearings 30 and 31 of which one may be located beyond the fans. In some cases the shaft support may be mounted on the inside of the inside or other wall of the kiln, or it may be mounted even outside the kiln.

In some cases, I prefer to provide suitable means for cooling the gears which may, for instance, consist of extension of surface radiation 58, of familiar use in the art, as shown in Figure IX.

In case an endless chain or rope 60, or individual motor 73, is employed, as it maybe, (see Figure V) to drive the cross shafts 2'1 and 28, the same may be located wholly or in part either inside or outside of the kiln.

In some cases, also, I place fans adjacent to the end doors or other doors of the kiln in such a way that a fan throw is made against the door, thus effecting a uniform pneumatic pressure against thedoor and conseqent di charge out through the crevices around the door in preference to effecting an intake of air therethrough. Thus, by building up pneumatic pressure at the door, admission or intake of cold air through the crevices is in large measure prevented with the result of a more uniform drying in the kiln operation. The fans may be driven by individual motors 62, in which case the same combination of opposite pitch of fan blades will be available through opposite rotation of the transverse shafts 27 and 28 to effect within each kiln compartment transverse movement of circulation.

The fans may be at discretion disposed overhead, at the side of the loads, or below the loads, as preference may dictate.

The coils 2021 may be heated by any suitable'means, as for example from'any preferred source of steam supply not illustrated. Power to operate the shaft may also be derivedfrom a source not illustrated. The stock loads of lumber 6 may be sta cked, if preferred, in any suitable or commonly used manner.

The drive mechanism may be, as already specified, by individual motor 62 for each fan, or by one drive system, such as one continuous rope 60, cable, or other flexible element, as illustrated in Figure V for example. In'other cases, eacli shaft mayhave a separate drive 62 for each individual fan, or any other suitable driving mechanism may be employed.

A plurality of two or more fans is designed to be employed in each kiln. If an odd number of fans is employed, the majority of them will be either right hand or left hand fans, and in that case the resultant throw of the combination fans may not be strictly transversely directed within the kiln, but the resultant throw may be directed towards the part of the kiln that is, without provision to the contrary, ordinarily coolest, by reason of in-drafts of outside air, excess loss of heat, and to outside exposure, or of other cooling factors.

I prefer to employ besides any usual system of heating coils 20 and 21, means for humidification 64 and any usual or preferred means for controlling the temperature and humidity within the kiln.

I prefer, also, to employ any usual means for admitting fresh outside air, for exhausting the kiln atmosphere, or for the purpose of ventilation. If overhead fans are employed, I prefer to provide fresh airports 66 and ventilators 67 on opposite sides of the respective fans at points of suction and pressure, respectively. The fresh air ports 66 and ventilators 67. may be located at points developed by them of maximum suction and pressure, but they may, if desired, be placed in any other suitable and desired relationship to the fans. For instance, they may be placed at points of maximum pressure in some installations and points of minimum pressure in other installations, depending upon the design of the kiln, the location of the fans, and other considerations. The fresh air ports 66 and ventilators 67 may, in some cases,,require air direction ducts in addition to mere ports.

My kiln may be either of the charge type or of the progressive type, the principles involved in my invention not being limited to any particular type of kiln. Furthermore, the principles of my invention may be applied to kilns having longitudinal as well as kilns having transverse circulation effected as by means of fans having shafts substantially parallel to the air flow.

In various embodiments of my invention, I prefer to employ partitions 52 between fans to prevent back-lash or short circuiting of air between fans instead of air flow passing through the stock loads. I also prefer to provide suitable baffies 70 and 71 at the ceiling and at the floor respectively, to prevent air from passing around the stock loads instead of through them, as preferred of course.

In the usual installation of any form of embodiment of my invention, the fans are mounted in close proximity either to the fioor 1 of the kiln, or to the roof 4. The space between each fan and the partition 5 varies in most-installations so as to provide a greater spacing between the edge or periphery of the fans and floor 1 or the roof 4 of the kiln than between the edge of the fans and the partition 5 of the kiln or the top of the stock load 6. This variation of the position of the fans in relation to deflecting surfaces permits each fan in rotation to deliver air in slightly variable direction in addition to the prevailing transverse movement of the air. This variable or longitudinal tendency of the air movement, in addition to the general transverse air movement, is known as throw and inasmuch as the fans are substantially all spaced equally from the side wall partition or stock loads within the kiln, the throw from a right hand fan is substantially equal and opposite to the throw of a left hand fan. By the change of direction, the. counteracting currents from the oppositely rotating fans substantially merge into one current before passing through the stock.

The usual fan throw varies in direction and extent. There is what may be termed a normal tendency toward a throw in most instances, and the counteraction of this throw is contem- One of the main objects of my invention is to provide for counteracting this fan throw as just specified. Such counteraction may be effected in at least one of two ways;-first, either by alternating right and left hand fans throughout the kiln; and, second, by placing right hand fans in series at one portion of the kiln and left hand fans in series at the other end or portion of the kiln. In the first of these cases, the tendency towards resultant throw or towards directed longitudinal circulation is substantially eliminated. In the second case, the series of fans in one, portion of the kiln may effect a resultant throw in one direction, but this would be counteracted by the substantially equal and opposite throw of the other series of fans in the same compartment of the kiln in another direction. Upon reversal of the fans, the resultant throw in each case would be substantially directed in opposite directions.

When an odd number of fans is used, the

odd fan is placed to throw additional air toward the part of the kiln that is normally the coolest.

This is usually the low' end of the kiln or the door end of the kiln when only doors at one end are used.

A simple means for driving the fans is illus-/ trated in Figures IV, V, and VI. -These figures illustrate alternately d.sposed right and left hand fans driven by-a common drive rope or chain 60, turning individual sheaves or sprockets 61. The rope or chain 60 is driven by suitable driving means as, for example, a motor '73. A suitable tension control-assembly 74 is employed, consisting, for example of a weight 75 for keeping'the belt 60 taut and so maintaining uniformity of tension on the drive rope 60 by means of a pulley 76.

Illustrated in Figures I, II and III is a drive shaft within a kiln having bearings at spaced intervals for rotating one or more fans, which shaft has a substantially fixed dispositional re lationship to the bearings or to the bearings and gears. There must be means for providing compensation for expansion and contraction of the shaft, and in addition thereto, for maintaining this above mentioned fixed dispositional relationship. This may be done in one of several ways, of which, for example, ,four are illustrated.

In the form of embodiment of my-invention illustrated in Figures I, II and -III, I employ, as

.aforesaid, a common longitudinal drive shaft 37 for the fans. At that end of the kiln where the motor is located, which, when a common drive shaft is used, may be, therefore, denominated the drive end of the kiln, I prefer to provide one thrust bearing Z7 which accommodates the shaft at that point which'is preferably close to the drive mechanism or motor '78. A result, substantially the same as that already described, is achieved in this kiln, insofar as right and left hand fans turn in opposite directions to deliver air in the same general transverse direction. The driving of the shaft may be accomplished substantially in the manner described above. In my system, it is necessary to provide means permitting compensation for expansion and contraction in a fan shaft such, for example, as the main drive shaft 37, so that no disturbance of the operative relationship between the driven fan and shaft is occasioned by shaft expansion or contraction. In the drawings, I illustrate four means of accomplishing this result.

7 For instance, in .Figures VII and VIII, I show a gear and shaft support having a base which may be for stability firmly attached to the sub-floor 5. The top part 81 of said base supports in constant operative relationship the gear case 44 and bearings 46 and 47, and is joined to the base by suitable means, such, for example, as'bolts 83, having each a cotter pin 84. When this type of bearing and gear stand is used, expansion or contraction of the main drive shaft 37, due to variation of temperature, effects a movement of the shaft by means of movement in the joints 85 and 86. In the normal kiln, which is usually less than 120 feet long, the maximum expansion or contraction due to change in temperature would be less than two inches, which would measure the maximum movement of the bearing and gear required at the end of the kiln opposite the thrust bearing.

In Figures VII and VIII, I show pedestal joints providing for movement of the shaft and its bearings, or its bearings and gears to allow expansion and contraction of the shaft 37. The shaft expansion or contraction is substantially uniform and the movement of the several bearings, or several bearings and gears, respectively, is proportional to the distance from the thrust bearing of the driven end of the shaft. amount of expansion, for instance, will determine its horizontal movement from the thrust bearing. Because the bottom of the pedestal is fixed, each bearing or bearing and gear will describe an arc of a circle, its travel being proportional to amount of expansion. In the case of any material amount of expansion or contraction possible in the operation of the kiln, the shaft will remain substantially straight because the are described by the bearing or gear having the greatest movement will not be great enough to materially affect the alignment of the shaft.

In Figures IX and X, I illustrate another compensating means for providing for shaft expansion and contraction. This means includes a sliding gear case 88 and its pedestal 89. In other words, when expansion or contraction of the shaft 37 permits .the gear case 88, which is fixedly attached to said shaft but is loose on its pedestal, to slide in the groove 90 of its pedestal 89, thus taking care of any shaft expansion and contraction that may occur.

This expansion and contraction can be compensated for and taken care of in a number of ways, for example, illustrated in Figures XI and XII. This third method of taking care of expansion and contraction of the shaft, consists of a jaw type coupling 92 mounted between intermediate combination bearings and gear cases 44 and 45. In this case the bearing pedestals 48 form rigid supports for the bearings and gear cases 44 and 45. Each gear case 44 and 45 is thus attached to a divided section of the shaft 37, each section being joined to the section adjacent by means of the jaw type couplings 92 with suiiicient clearance 93 between halves of the couplings 92 and ends of the shafts, to provide for requisite expansion and contraction in each section of the shaft.

Right hand and left hand worms may also be employed for accomplishing the same compensation for expansion and contraction of the shaft, as shown in Figure XV. The worm 68 is long enough to permit maximum expan- The" sion of the shaft 37 and still permit engagement with the worm wheel 69.

The worm wheel will drive the transverse shafts, comparable to shafts 27 and 28 in Figures VIII and IX. y

In all cases where a common drive shaft 3'7 is used, the fans move with the shaft and provision must be provided for this movement in the fan housings. Any preferred method may be employed for this, for example, I have illustrated a fan housing slightly large to provide plenty of space for the movement of the fans due to expansion or contraction. The fan openings may be elliptical.

Any preferred housing for the fans may be used, such for example, as stream lined, band housing, or plain openings in the partition.

It is to be understood that the compensation for expansion and contraction of the shaft may be employed in other instances than those illustrated. For instance, it may be employed, if need be, for a shaft having fans mounted directly on and rotated directly with the shaft.

If more than one common drive shaft, or series of transverse shafts, is used, all the resultant throw of all the fans would be coordinated to effect the most effective and uniform drying conditions.

I prefer to provide suitable baffles 70 and '71 which prevent the circulating atmosphere from evading the loads in making circuit.

I also prefer to provide suitable fresh air intake ducts 94 and ventilators 6'7 of any form preferred, such, for example, as those well known in the art. When the fans are located below the stock loads as shown, for instance, in Figures IV, V, and VI, fresh air ducts 94 having intake doors 95 opening to the outside of the kiln and ports 96 opening at each fan, are preferably provided. It is to be understood that when the circulation is in one direction, the air duct on one side of the fan supplies fresh air, and when the circulation is reversed,

- the ports on the other side of the fan functionate by substitution for the .ducts. In each case the fresh air duct or the port on the suction side of the fan is employed to admit fresh air into the kiln. When the fans are placed above the loads, as shown in Figures 1, II, and III, I prefer to provide ports on. opposite sides of each fan which act either as fresh air ports or as ventilators 66 and 67, respectively, according to the direction in which the air of circulation is moving. When the air is passing in one direction, the ports 66 act as fresh air intakes and the ports 67 on the opposite side act as ventilators. When the circulation is reversed, the relationship of the fresh air ports and ventilators is correspondingly reversed. It is understood that in kilns having fans above the stock loads, the roof construction may be flat, arched or gabled, to provide stream line air guiding surfaces if desired.

The operation of the kiln requires the setting of the fans in motion to deliver in effect air in one circuit of transverse circulation throughout the kiln. Fans rotating in relatively opposite directions counteract any tendency towards unequal effective distribution of circulation.

As the kiln-becomes heated up in operation, the line shaft 37 tends to expand. This is compensated for by means already described with reference to Figures VII and VIII.

It is my intention that this invention be not confined to the exact designs shown, as there are many ways of carrying out the same principles which will readily suggest themselves to one skilled in the art. Therefore, it is to be understood that this invention includes within its scope whatever arrangements come within either the terms or purview of the following claims.

What I claim is:

1. In a dry kiln, right and left hand fans, each of said fans effecting independently by'delivery of an air current circulation of the circulatory medium through the interstices of the stock loads in one circuit of continuous circulation, right hand fans turning in opposite direction from the left hand fans.

2. In a dry kiln comprising circulating means distributively mounted in series throughout the length of the kiln on separate shafts, a common drive means for said shafts, said circulating means consisting of right and left hand fans turning in opposite directions for effecting one substantially uniform circuit of air circulation through interstices of stock loads within said kiln.

3. In a dry kiln comprising circulating means mounted on separate shafts, a common drive means for said shafts, said circulating means consisting of right and left hand fans operatively mounted substantially in one plane, said fans turning in opposite directions for effecting one substantially uniform circuit of air circulation through interstices of stock loads within said kiln and meansof providing compensation for expansion and contraction of said shaft.

4. In a dry kiln, right and left hand fans alternately disposed within the kiln, right hand fans turning in opposite direction from the left hand fans, all of said fans effecting circulation of the circulatory medium through the inter-, stices of the stock loads in substantially one circuit of circulation.

5. In a dry kiln, right and left hand fans disposed respectively in series at opposite ends of the kiln, right hand fans turning in opposite direction from the left hand fans, all of said fans effecting circulation of the circulatory medium through the interstices of the stock loads in substantially one circuit of circulation.

6. A dry kiln comprising within it a drive shaft, a thrust bearing for said drive shaft, a plurality of gears fixed at intervals along said shaft, a journaled bearing for said shaft, a plurality of driven shafts at right angles to said drive shaft, each supported by a bearing and having a gear fixed thereon operatively enmeshed with and driven by one of the gears fixed on said drive shaft, a case for each pair of'gears, a support for each of said cases, a fan on each of said driven shafts, means providing for expansion and contraction of said drive shaft and maintaining variable longitudinal relationship of said cases on their supports and constant operative relationship between each pair of drive and driven gears, whereby said fans are rotated in either direction independent of expansion or contraction of said drive shaft due to variation of temperature within said kiln.

7. In a dry kiln, a partition, a right hand and a left hand fan operatively disposed in openings provided in said partition, each of said fans effecting an individual circulation, the right hand fan rotating in the opposite direction from the left hand fan whereby one circuit of continuous circulation is effected through interstices of stock within said kiln.

cases, means providing for variable movement of said cases, a partition in said kiln having openings therein for the accommodation of-said fans, and means for maintaining a substantially constant longitudinal relationship between the gears of each of said pairs whereby a variable longitudinal relationship exists between each of said-fans and its respective opening in said partition depending upon the expansion and contraction of said longitudinal shaft.

I JAMES FORREST COBB.

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